Lithium battery pack puzzle; advice please.

Thread Starter

Phil Russell

Joined Dec 21, 2014
19
I wonder if someone can solve a puzzle for me? I bought 2 generic 18v lithium ion battery packs (4Ah) for my Ryobi drills. One works fine. The other, when I put it in the drill on receipt just produced a 'click' and minute chuck movement. Thinking it was not charged, I placed it in my charger (correct one) but it said fully charged after about 5 minutes. I noticed a set of green bars on the battery on a push switch; pushing the switch lit all green bars indicating fully charged. I checked battery voltage: 19.2v. The battery also fails in another drill and by moving batteries between drills I can rule out drill contacts. But at times the battery worked and continued to do so with 'on-off' sequences of the drill trigger until the drill was left for maybe 10 minutes, when the click resumed. I then noticed that if I pressed the charge check button on the battery, and then immediately the drill trigger, the battery worked .. it even worked if I waited for the green lights to go out and then pressed the drill trigger. But wait about 5 minutes and ... click.
Now I thought, in my ignorance, that battery packs were simply batteries in series but clearly there is more to this pack than that. A photo of a part stripped Makita pack shows a circuit board so I assume my Ryobi generic will be the same.
So ... can anyone explain to me what might be wrong with this pack?
Many thanks in advance
Phil
 

Thread Starter

Phil Russell

Joined Dec 21, 2014
19
Take it back for warranty replacement.
Yes, I agree that is the best option and one I am pursuing. I am not intending to delve into the pack but am curious as what the fault may be. It's just that I like to understand these things, as far as I am able.
Regards
Phil
 

crutschow

Joined Mar 14, 2008
25,269
Lithium battery packs often have internal circuits to shut it off and protect it from over discharge. It may be that the over discharge circuit is not working properly.
 

Thread Starter

Phil Russell

Joined Dec 21, 2014
19
Lithium battery packs often have internal circuits to shut it off and protect it from over discharge. It may be that the over discharge circuit is not working properly.
Ok, thanks. My 'lay person' interpretation of this is that the discharge circuit prevents too large a discharge load being applied (?) but that it may be faulty and hence operating at a lower load than it is meant to. Maybe ... but at present I do not understand how this would be bypassed when the 'check charge' button is pressed to reveal the state of battery charge .. green bars that light up. With the lights 'green' the drill bursts into life as if nothing is wrong.
Cheers, Phil
 

crutschow

Joined Mar 14, 2008
25,269
My 'lay person' interpretation of this is that the discharge circuit prevents too large a discharge load being applied (?)
No.
It prevents the battery from being discharged below a safe point (where the battery is considered fully discharged).
Over-discharge can ruin a lithium battery.
I do not understand how this would be bypassed when the 'check charge' button is pressed
That is odd, but pressing that may somehow signal the discharge circuit that it's okay to continue battery operation.
Still sounds like a faulty discharge protection circuit.
 

Thread Starter

Phil Russell

Joined Dec 21, 2014
19
No.
It prevents the battery from being discharged below a safe point (where the battery is considered fully discharged).
Over-discharge can ruin a lithium battery.
That is odd, but pressing that may somehow signal the discharge circuit that it's okay to continue battery operation.
Still sounds like a faulty discharge protection circuit.
Ok ... I am getting the message now, I think. So if the discharge circuit sensor 'thinks' a voltage of 19.2 volts (which is what I measured it at with a multimeter) is too low when under load (the drill trigger being pressed) and close to the damage voltage, it would shut off the power supply to the drill. But the battery check (green lights) would be a minimal load so not trigger the discharge circuit ... maybe even keping the circuit 'open' to allow the drill to operate.
Hmmm. I wonder (??) if I can safely rig up a circuit to check voltage across the battery terminals when it is on the drill???? Presumable it would drop to zero as soon as I tried to start the drill. I guess the multimeter in parallel with the drill contacts would do it? Or am I risking life and limb?
Cheers, Phil
 

crutschow

Joined Mar 14, 2008
25,269
You should be able to delete a duplicate post.

There's no problem with measuring the voltage for either the battery or voltmeter.
Just don't accidentally short the battery when doing the measurements. :eek:
 

Thread Starter

Phil Russell

Joined Dec 21, 2014
19
You should be able to delete a duplicate post.

There's no problem with measuring the voltage for either the battery or voltmeter.
Just don't accidentally short the battery when doing the measurements. :eek:
Thank you ... duplicate deleted.
I just connected up the multimeter to the battery while it was in the drill. Normal voltage recorded (19.2) until I pressed the drill trigger when voltage almost immediately, fraction of a second, fell to zero.
Tried again but after pushing the check charge button and while lights were green .. drill started and ran with voltage at 19.2.
So, mission completed. The explanations all make sense, thank you for your time and patience. I guess the replacement of a faulty part is not really a diy job? but never mind as the battery could well be used if I push the 'check charge' button each time ..... ?

Once again, thank you.
 
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